28 October, 2014

DIY: Turn your bike into an e-bike for yourself in 5 steps - Step 1: Build the battery from recycled laptop batteries

BH bike modified to electric with prokit 901; a real pleasure to climb hills with it
Some time ago I had in mind to change my bike to convert it to an e-bike; it was increasingly more difficult for me to climb the hill to my home with sections of 14% and get sweating profusely in summer is not very comfortable to say something.
In the next 5 entries I will tell you the details of how I have adapted mine for 500 € (if you want it without complications, since you have € 1100):

1: We'll see how to prepare the battery with Li-ion 18650 batteries

2: Putting the engine on the bike

3: Preparing the housing for the batteries in the box

4: Connecting it all and programming the controller

And finally, it is important to have good brakes; Bike weight reaches 25 kg.

Voltage monitor cell; important to know the status of each pack

The truth is that when you live between 2 and 10 kms from work, an electric bike, zero emission, less maintenance than a more manageable and cost motorcycle, is an option that fills you with satisfaction every time you use it. However, to make it legal, you have to limit the power of 250W, 25 kph top speed and work only when you are pedaling. Although it seems a bit absurd about the law especially if you live in an area of high hills terrain, the speed should be limited to 40 kph for bikes, limited braking distance and go (without motor, someone unprepared is difficult for him to maintain that speed).
Sebastian Reyes was informing me about the kit was best for me; I recommend taking a look at your blog, for example this post where you information and advice on power kits available engine types, etc before you decide for your own.
The kit can be purchased at kitelectrico.com or Electrorodes.com for example, which is where I took the PROKIT 901 ; Paul greeted me kindly and solved some doubts. In GoldenMotor Spainis also available (and cheaper, and that is the same company). China ruled ask directly; the final cost and management of potential problems by not advise shipping costs.

I was also looking for information on the net (at Endless Sphere You can find plenty of information in English about electric bikes) and a priori value with a simple help me so that my girl is also encouraged to take over the bike, I did not want fanciest too.
The most basic kit 250W (motor, controller and handles) in July cost about 280 € without battery, but then I was finding out about such small engines and often wear nylon parts degrade over time, apart from some powerful and not have regenerative braking, so that the advantages of discretion, legality and price is quite blurred, in the end I decided on one engine more powerful Chinese Brush Golden Engine, the Prokit 901 without much lasting mechanical parts and I help more effectively with uneven, leaning on downhill braking (brake pads saving step) and more flexible in terms of power for the future.
We also have the option of putting two low power motors on both wheels, but nothing comes to mind.
In the next post we'll talk in more detail the types of engines used on a bike.

Building your own Li-ion battery

You'll see that the battery is the most expensive part of an electric bike; one avg Li-ion 36V and 10Ah costs from 350 €, so I decided to save myself quite the same building it from laptop batteries used and incidentally learning a lot in the process, my inspiration from other bloggers as Jacopo Rodigari they did so successfully . As you can see, I will build 180 € approx. a Li-Ion 18Ah (9x2.000mAh packs x 10 connected in series) battery.
First of all my apologies to Pamplona Mikel, who told me years ago the idea of using old laptop batteries to build a battery for an electric bike, guess ya gotta do, I hope you can read this post and leave a comment sometime :).
The importance of "C": Download Speed
We must also appreciate that these batteries typically have rate discharge / charge 1C ; ie willload / unload safely in one hour (if the battery has 2000 mAh capacity, then you can deliver 2 amps in one hour safely without damaging it), and although they are much more convenient in the long run for LiFePo4 that allow download rates from 15C to 25C, and doubles the life of 1000 cycles typical of portable reaching LiCoO2 last up to 2000 cycles, its price may rise to 600 € a 12Ah, when we see that we can do a 18Ah for less than 150 € recycling dead batteries.
In any case, if we want a new battery, we decantaremos by the LiFePo4 for the bike, as they are much more durable and powerful; higher price is quickly offset.
Example: If we have a 2.2 Ah battery and 5C discharge rate, we have: Discharge Rate = 5 * (2.2Ah) / h = 11A -> The maximum current that a battery can deliver 11A is (obviously providing that intensity only you will last 12 minutes).
We have to assess the ability / instantaneous power we want to have. This is given by the number of batteries we put in parallel in each cell, and the rate of discharge of the type of batteries used. A greater number of cells in parallel in each pack (as discussed in a previous entry ), we will take more and more power / amps can squeeze in a given time.
If the routes are going to be short or have limited space on the bike (I chose the picture for better balance the weight and be safer, but can also mount the battery on the rear rack or front),we decantaremos battery-less cells, even we can mix LiPo batteries (up to 30C discharge rate and same voltage range than LiCoO2) with Li-ion to have a little more power, provided they have the same capacity.

In this case I wanted to have it both ways; usually short trips but with high energy demand (difference of 50 m with slopes between 7 and 14%), so I needed to put at least 8 batteries in parallel to get 26 Ah instant without damaging the batteries (they are usually battery 2600 mAh so you can ask 3 Ah for each without damage.
Finally, for configuration and space, I leaned LiCoO2 battery packs 9 (9x2,6 = 23.4 Ah), ie, I have 23 amps in one hour, which I believe will last me three trips.
It is very important to not ruin the battery prematurely, not demand more power than that for which they are prepared.Emptied in less time than recommended assumed temperature rise and changes in internal chemistry, minor damage that accumulate and reducing its life useful. To avoid this, as we shall see in future entries, program the controller to ask just amps the battery can deliver comfortably (as we do with regenerative braking, not faster recharge the battery support).
In my case the PROKIT 901 runs on batteries 24, 36 or 48V (the higher voltage higher top speed, higher RPM) for 36V need 10 cells (10 * 4.2V = 42V), making a total of nothing more and no less than 90 batteries 18650!
New (Samsung, Panasonic or similar) usually go for 3 or 4 €, which would leave a total of 360 €, which in this case should go directly to the LiFePo4 (with voltage range of 2.5V to 3.7V fully charged).

Must take into account the influence of the voltage on the speed. Direct brushless (3-phase) are low revolutions per minute (RPM), maximum RPM are given by the voltage; the higher the voltage higher top speed. With 36V the Prokit 901 (GoldenMotor engine 46 pin) could reach 35 km / h, but if we wanted more speed (which would not be legal in Europe) need to build a battery voltage.

Why not Lipo? Both chemicals are similar in terms of power and weight, but we opt for LiFePo4 electric vehicle. The main difference between them is that the LiFePo4 live longer (up to 2000 cycles), much safer and a lower voltage range (2.5 to 3.6V) while Lipo are shorter longevity (from 100 to 500 cycles), more inexpensive and light, and have higher C (up to 60C, the most dangerous) and range much like the LiCo voltages; between 3.2V and 4.2V minimum maximum, the Lipo is ideal for Radio Control.
To get the 90 batteries I resorted to selling second hand, and I was lucky to find many laptop batteries for sale on Ebay by anyone else outbid, so I could get packs of 6 batteries in good condition for 8 € (so that each came out to 1.3 €):

The worst I saw battery: 2200 mAh only 4 new "fake" plastic batteries.
Some are easily disassembled with a flat screwdriver (you can find videos on Youtube), but others are so well assembled that I had no choice but to use the dremel to help me open them, cutting the union of the sides carefully the cutting wheel does not touch the batteries:

Notice the temperature safety devices bearing the battery eg Gray cuts the current flow if heated above 80 ° C; I kept it for use later in my drums:

Curious battery, flat cells that I could take to a remote control car.

To quickly check the status of each battery, I used the versatile and economical iMax B6 , and many of them did not have to download them completely to see their approximate capacity; ifonce charged to 4,1V and leave after two hours at rest (important), if they have not lost voltage check with 1A discharge over hold under load to 3,9V, having downloaded more than 100 mAh, we can be sure to reach and pass the required 2000 mAh (which would be approx. 80% of the capacity of new or more).
I've run on batteries, though the charging cycle and discharge showed a capacity of 1750 mAh, internally were damaged and lost its load in a few hours, hence the importance of removing them a few hours and check the voltage before and after; there can be no more than 0.01V difference or not serve us.

Let checking batteries; the top row are more than 1900 mAh capacity each
I got 12 batteries of laptop from different parts of Spain and each contained between 3 and 8 Li-ion 18650 each only 2 full batteries were unprofitable for this project (with capacities of less than 1300 mAh), but I could use in another project with less battery capacity demand.
These, added to the 14 new units already had 2400 mAh, just got to assemble the complete battery.

This charger will allow us to recharge batteries quickly revive even though the iMax B6 reject these "charge too low"

The shape of the battery 
We will build the battery with the format that suits us for the site we have. At first I had thought to take advantage of an aluminum box with a large hard drive, but it was small. Then I studied the space I had in the box to the battery, and I decided to bring it along with a width of 3 nested stacks between itself so would have a width of 5 cm., with the width of my box area would legs of 4.5 to 6 cm. approx. with lids.
My BH Jumper has a reinforced aluminum frame very small, ready for jumps (of which I can and forget to put batteries), so had to plan well your disposal.

In the following video you can see how your battery has built Jacopo:

In the following video you will see how I attached silicone batteries (not flammable, hold high temp.), And then how I soldier, with some tips to consider:

As you can see, there are 10 packs in series of 9 parallel batteries each, glued with silicone to each other, so that each pack fits the following (very appropriate to maximize space and fit together in its final accommodation bike).
We assemble each pack with a capacity as closely as possible to the rest ofthe discharge and charge remains tied between packs during use and recharge.
Keep in mind that each battery 18650 has unique characteristics that differentiate them from the rest, depending on their quality and use; internal resistance, capacity, etc. The same battery from usually very similar. I mixed all delivering the best and worst among all the cells; still, as we see in the video below, the cell 10 has been somewhat higher than the rest, and 7th much lower, so I'll have to check it, replacing one of their "batteries" so that it can deliver the same power as the rest because right now can not meet demand, causing differences in the loading and unloading.

On the other hand, is not worth any power to unite us, but must be properly sized diameteraccording to the electric current passing through them; to calculate the cable should be between the packs can use this handy calculator . Between each "battery" 18650 we can use more fine wire, connecting each cell with more than one contiguous to ensure proper transfer of electrons. 
When soldering to batteries, see that they do not catch a lot of heat (more than 20 seconds with a tinker 32W is not recommended), excessive heat damages the battery. 
Here's a video of another "handyman" riding packs of 6 and checking them. 

In the next picture you can see that the packs I've attached directly to test with it (upload and download), but it is best to facilitate maintenance, placement, etc. is placed right quick connectors for the intensity that we manage.

To do this I cut the connection cables, always helping us come good of heat shrink tubing to insulate:

Then the tin-plate:

And I've finally put the male connector on the positive side of each pack, and the female on the negative, as a reference, and tinned tight to ensure good contact: 

If you have any problems, short for whatever reason (lack of privacy, unwanted connection, etc),we can prevent something worse (fire, damage to the battery, etc.) by placing a fuse car amid the larger battery amps that we will use:

With these connectors we can put the removable fuse:

Making quick connectors (yellow); Outside the heated PVC plastic to make it tighter and fixed:

Another point to keep in mind is the proper use of the battery; Each pack should not lose 3V or 3,1V load at rest, because with that voltage battery retains only 5% capacity; by its nature, this type of chemistry they suffer more when there is less than 20% or when kept charged above 80%, reducing the number of cycles of useful load, which as we discussed earlier in the cobalt used in laptops, 1000 cycles are theoretical.

Tips on use and conservation of Li-Ion batteries (LiCoO2 chemistry)
Summarizing, portable batteries are "cell" model 18650 with the following characteristics (width 18 mm and length 65 mm..):
  • High energy density (the most).
  • Not discharging faster than 1C (forget loads in less time than 1 hour).
  • Never download below 3.0 volts, and if discharged below 3.5V, load Immediately;discharge below 3.5V or leave discharged below this value shortens your life; it is preferable to leave it partially charged (not partial loads damage, but comes to them better than a full load).
  • Never charge above 4.2V (recommended not load above 4,1V therefore, if we load always 4.0V tripled its useful life).
  • The voltage at rest indicates charging ; to 3.5V are empty, and under load it is advisable not to lose 3,1V. Unless degraded 3V lithium crystals formed quickly, breaking down over the longer they are empty:

  • If we appreciate that very hot when loading or unloading, do something wrong or is damaged; battery is suffering; the higher working temperature lower lifespan.
  • If not you will be using for more than a week, let them charged to 3,8V is the optimum storage charge.
  • Over-discharged batteries can back to life in some cases (especially if they alone eventually they were emptied, often downloaded 1% monthly).
The relationship between the load voltage and load cycles (cycle life)
The battery has a very high cost to not care for; the lithium, but have no memory effect, they do have an interesting feature, the less the upload, the remaining number of cycles increases exponentially according to the following formula (roughly):

Vf (VAC) = 2 ^ [10 * (4.2-Vac)] (Vf is the factor of improvement in life cycles, and Vac is the charging voltage)
If these batteries for normal accepted 1000 charges, if ever recargáramos 3.9 volts, could recharge 8,000 times instead of thousands.

But more important not load too much, let's not completely discharged; to prevent that and use them optimally (for the price we better) I was looking to put a pair of monitors economic burden , each monitoring five cells, with an audible alarm that can be set to 2.9V as a warning if any cell reached that minimum.
As I did not like the look (the voltages are happening on screen) and what they consumed, replaced it with another system as I mentioned before:

Excluding batteries
Finally it is important to isolate each well pack or battery part, to avoid any possibility of short circuit or other metal parts of the bike, as well as preventing water from entering the same(although as discussed in other entries, former is prevented from entering the battery compartment).
CAUTION DANGER: If not properly aisláis batteries, especially those who have plenty of instant download, in case of a short circuit (for positive contact with unintended negative), the battery will heat up quickly, damaging and may reach in flames!
Despise not properly insulated from all metal surfaces of the bike, starting with the wrapping of each pack. I used white, economical and durable duct tape:

Adjust the belt to the shape of the battery to allow engagement with the rest. Before you insulate well worth examining your accommodation on the bike, and see how we can hold them, checking that all come and how best to tie them, as we shall see in the next posts.

And we would have the battery ready, but it's no use if we can not load; need a good charger:

Loading the pack safely 

With a 41V charger and 2 Amp. for a battery of 18 Ah Li-Ion, we can fully charge in nine hours.As each pack having different total capacity and internal resistance, the charges tend to desigualarse between cells over time, thereby preventing a BMS, equaling the load balancing between all cells. As for now I have BMS, I prefer monitoring the load the last 2 hours making sure that no loads over 4,1V, because in the worst case could end up with a battery in flames .The first two charges were pretty good, with a delta of 0.1V between cells, but as the go recharging, and after about 4 or 5 refills, there is a growing gap between cells; indicative of the substantial difference in internal resistance between the cells.
It is very important to ensure that no cell is overloaded above 4.2V and it is recommended not to exceed 4,1V; when charging above 4.30V, the cell accumulates lithium metal plating on the anode; the cathode material is transformed into an oxidizing agent, becomes unstable and releases oxygen, progressively degrading the cell.

Smart Charger 2 Amp switched. and 36V model MCR0236L

In order to avoid that, I bought a BMS (load balancer) I had to return because it did not work as expected; batteries not load anything (was not able to match such a charge difference):

Testing the BMS (in this picture the wires were still connected properly)
Without BMS reloading will tend to accumulate the voltage differences between the different resistance cells desbalanceándose faster the larger the difference.
The issue of charging each cell at the same voltage is quickly complicated. Normally load balancers economic deliver maximum 300mA per cell, which causes an unbalanced load battery can last for days.
Much has been said in the forums on this issue. Some propose to use independent circuits DC-DC (available in China for 2 € each) for each cell, regulated voltage to 4,1V, which would make a load balanced 2A child's play, and I think that is the way to go, perhaps in an upcoming project.Jacopo has even made ​​one to 1 or 1.5A load , much less limited than there are on sale for bicycle / electric bikes .
Even if we have time, I think we can use one like this to meet loads whenever you need to see: 

But its price, customs, rises to 140 €, so it may be best to seek a financial BMS that meets the task, or put two imax B6 separating the battery in 2 packs of 5 when it needs to load, and balancing a time. 

And this is all about the battery recycled Li-ion batteries, I hope you enjoyed as much reading as I prepared the battery;), if you follow these tips you will have battery for a while, in the next post we will place securely engine bike, and go into detail on the operation of these small wonders of science. 

ATTENTION: Disclaimer: These instructions are shared "as is", with the sole intention of sharing my experience, please refrain from implementing them if you do not have adequate means and knowledge, I will not be responsible for any consequence or damage arising . 

Sources of information: 
Endless Sphere : Source of essential information about electric bikes. 
Substituting plastic bushings engine Ba-Fang 
How to build lithium packs safely 
HobbyKing balanced charger for batteries up to 10 packs in series 
Testing 18650 Li-ion batteries of various brands 
Anatomy of a Li-ion battery with protection circuit 18650 
Technical details of the charge and discharge batteries by type 
Monitor voltage 8S HobbyKing 
Charging Li-ion batteries 
The Prokit 901: Technical details and interior 
The lithium-ion (Wikipedia) 
Details batteries LiFePO4 
Electric cable diameter calculator


  1. ¿Que tal te funciona la bici? ¿sigue funcionando correctamente o hay algo que se pueda mejorar de lo ya expuesto para mejorar su durabilidad o funcionalidad?

    1. Muy bien, le cambié las baterías por LiFePo4 para más potencia y durabilidad (aunque menos autonomía), y no dejo de hacerle mejoras...